The present invention relates generally to bearings which provide damping and support between two relatively moveable members, and more particularly to an improved spring support for a self-pressurizing compliant hydrodynamic gas bearing which exhibits a nonlinear load-deflection characteristic useful in controlling shaft dynamics, such as occurs with small, high speed rotors utilized in gas turbine engines.
Compliant hydrodynamic gas bearings are ideally suited to conditions found in high performance machinery subject to extreme conditions of temperature and speed. Such bearings are not subject to significant operational and durability limitations characteristic of bearings which require liquid lubrication and complex lubricant, support, cooling and sealing systems. Hydrodynamic gas bearings provide better performance while simplifying the bearing structure.
Typically, hydrodynamic bearings comprise a housing which supports a relatively large journal or shaft diameter therein. A comparatively small running gap separates the inner diameter of the housing and the outer diameter of the journal. Typical hydrodynamic bearings further employ a spring mounted damping structure within the running gap to facilitate management of manufacturing tolerances and journal deformations due to centrifugal and thermal displacements without detrimental changes to the required bearing tolerances.
As shown in FIG. 1, one known hydrodynamic gas bearing structure 10 comprises a set of tilting pads 12 radially positioned around a journal 14 by a set of bars 16 machined or affixed to the inside of a bearing housing 18. A set of sheet metal segments 20 are positioned between the bars 16 to provide a spring support for the tilting pads 12, thereby achieving static and dynamic load-bearing capabilities relative to the journal 14.
However, the known hydrodynamic bearing 10 shown in FIG. 1 only provides a constant spring rate bearing support over all load conditions. Referring to FIGS. 2A and 2B, the tilting pad 12 contacts about a third of the arch length at the center of spring 20. Tilting pad 12 is designed with reliefs at both ends such that the amount of contacting surface area does not change over the applied load force F. Thus, spring 20 only exhibits a constant spring rate (i.e. linear load-deflection characteristic) until the back of spring 20 would contact housing 18.